"Tens of thousands of students have contributed to a database of over 120,000 acceptances at hundreds of colleges in the US. Using a formula similar to the one used to rank chess masters, Parchment helps decipher the meaning of those student choices," according to the methodology details. "When students are admitted to multiple colleges, they must choose just one to attend; this reveals their preference for the chosen school compared to the other schools that admitted the student but were not chosen. After observing enough of these decisions, we can rank the colleges based on the students' revealed preferences."